In the closing days of World War II, the United States was facing a difficult decision. In the face of increasingly fanatical Japanese resistance during the island-hopping Pacific campaign, American casualties were increased dramatically. 

Fearing that an invasion of Japan would cost hundreds of thousands of U.S. casualties and millions of Japanese, the decision by President Truman to drop the atomic bomb on Japan was not made lightly. The atomic bomb was dropped at Hiroshima and Nagasaki. According to some estimates, more than 226,000 people, mostly civilians, died in the two blasts. Following the bombings, Japan surrendered. It was the only time that nuclear weapons have been used in war. 

By August of 1945, there was little doubt that an invasion of mainland Japan was going to happen. The Japanese had been pushed all the way across the Pacific, had their war industries smashed, and were starving. But they weren’t yet defeated. Although they still controlled parts of New Guinea, the Dutch East Indies, and Indochina, their forces there were cut off and had no hope of coming to the assistance of the Japanese islands. 

The “Little Boy” atomic bomb.

The Japanese still had massive numbers of troops in China but defeats in the Philippines, the Marshall Islands, Iwo Jima, and Okinawa had the U.S. on their doorstep. B-29 bombers could now hit Japanese cities and were close enough to have fighter cover all the way to Japan and back. But those American victories were very costly. Where Japanese casualties had been five to six times that of American troops earlier in the war, by the time Okinawa was finally secured in June 1945, the ratios had dropped to 2-1. Japanese troops would rather fight to the death than surrender. Since the battle of the Philippine Sea, Japanese suicide pilots (kamikaze), had also been taking a toll on American warships and lives.   

In preparation for the planned invasion of Japan (Operation Downfall), the B-29 raids over Japan went from high-altitude precision bombing to low-level area bombing with incendiaries. The aim was to destroy the Japanese war machine by targeting the industries. In many of the largest cities in Japan, most buildings were of paper and wood. The results of the fire-bombing were horrific. Over 100 of Japan’s largest cities and towns were firebombed by June. Just in one bombing of Tokyo, over 100,000 people died. Japanese firefighting equipment was not able to keep up. 

With estimates of U.S. casualties in the planned invasion ever increasing as the Japanese rushed troops back from China and created more homeland divisions, the U.S. decided that the atomic bomb would be attempted. There were even proposals of using poison gas on the Japanese, as well as dropping it with a warning in an unpopulated area but those proposals were rejected. The U.S. created the 509th Composite Group, commanded by Colonel Paul Tibbetts to conduct the drops.

See newly declassified photos of the atomic bomb dropped on Hiroshima

Read Next: See newly declassified photos of the atomic bomb dropped on Hiroshima

The components for the bomb were delivered by the USS Indianapolis to Tinian on July 26. Fearing that a crash upon takeoff would result in a nuclear explosion, Tibbetts had the engineers modify the Little Boy bomb design to incorporate a removable breech plug that would permit the bomb to be armed in flight.

After the Japanese rejected the Allies’ surrender demand, the mission was given the green light. The primary target was Hiroshima with Kokura and Nagasaki as alternative targets. Tibbetts piloted the B-29 “Enola Gay,” named after his mother. The plane belonged to the 393rd Bombardment Squadron of the 509th Composite Group. 

Tibbetts took off from Tinian accompanied by two other B-29s, “The Great Artiste,” which carried instrumentation to measure the blast, and “Necessary Evil,” which served as the photography aircraft. The flight from Tinian to Hiroshima took six hours.

The three aircraft rendezvoused over Iwo Jima and headed for Hiroshima, where they arrived in clear conditions. At 08:09, Tibbets started his bomb run and handed over control of the aircraft to his bombardier, Major Thomas Ferebee. He released “Little Boy” at 08:15 local time exactly as planned. The nuclear bomb containing approximately 141 lb of uranium-235 took 44.4 seconds to fall from the aircraft, flying at about 31,000 feet, to the planned detonation height of about 1,900 feet above ground level (AGL). Immediately upon releasing the bomb, Enola Gay turned away and went into a steep dive to get away from the blast. It traveled 11.5 mi before it felt the shock waves from the blast.

The aftermath of the atomic blast at Hiroshima.

Due to the crosswinds, the “Little Boy” bomb missed the aiming point, the Aioi Bridge, by approximately 800 feet. It detonated directly over Shima Surgical Clinic. The blast was equal to 16 kilotons of TNT. Its radius of total destruction was about one mile, with resulting fires across 4.4 square miles. Because the bomb exploded above the city, the blast was deflected down rather than outwards. So, several of the reinforced concrete structures remained standing. 

Onboard the Enola Gay, the crew was shocked by what they saw. They had never before seen such enormous power unleashed by a single weapon. On the ground, Japanese survivors reported seeing a blinding flash followed by a tremendous explosion. Of the approximately 350,000 people in Hiroshima on the morning of August 6, upwards of 70,000 were killed immediately or died in the resultant firestorm that engulfed the city. Another 70,000 were wounded. Nearly 70 percent of the buildings in the city were destroyed. Of the Japanese soldiers stationed in the city, 20,000 were killed including nearly 3,250 troops conducting physical training on the parade ground near the epicenter of the blast.

The Japanese High Command knew that Hiroshima had gone silent. But since they knew of no large air raid having been conducted there they sent a scout plane to report back to Tokyo. The pilot reported that the city had been destroyed by some new type of bomb. The Japanese government was still in the dark about it until some 16 hours later when President Truman addressed the world on the radio. 

Truman ended his broadcast with a chilling warning to the Japanese to surrender: “If they do not now accept our terms, they may expect a rain of ruin from the air, the like of which has never been seen on this earth. Behind this air attack will follow sea and land forces in such numbers and power as they have not yet seen and with the fighting skill of which they are already well aware.”

The Japanese High Command thought that the United States would only have enough material to make one or two additional nuclear weapons and thought the country could withstand it. With silence coming from Tokyo, the decision was made by Truman to conduct a second drop. 

On August 9th, the “Bockscar” a B-29 commanded by Major Charles Sweeney, dropped the “Fat Boy” atomic bomb on Nagasaki. The United States planned on dropping another nuclear weapon on August 19th, three more in September, and three more in October. Luckily, the Japanese surrendered, despite severe disagreements within the government to continue the fighting. Their surrender saved countless lives. 

The world had entered the dangerous nuclear age.